Pain in the XXXX

You really know how bad your back
When you cannot tie your own laces.
Little girls, with their teeth in braces,
Laugh at the pains that your body wrack.
If, invited by a girl in bed to frolic
You'd better say that you've got colic.

Agony, every time you try to pull on a sock,
And the way your underpants you have to throw
Into the air, is enough for everyone to mock;
How funny it is to see you catch them on a toe,
But it really descends into farce
When you try to wipe your arse.

You can't lie down on your bed,
You can't sit up in your chair,
The pain echoes round your head,
And it is hell to climb the stair.
This is when, despite being so well hung,
All you can give her is your tongue.

(OK, I know that when I changed the line order in the first stanza I mucked up the rhyme pattern so stanza 1 is now ABBACC and the other two are ABABCC but I don't think this interferes with the poem too much - form or function, everyone? Nb The English use of 'arse' is intended, Americans would say 'ass' as in 'donkey', but that wouldn't rhyme).